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93 we’ve installed,” said Andy Hughes. The sensors are based on the company’s patented vibrating structure gyroscope technology. The silicon MEMS ring in the sensors resonates at its natural frequency; the rotation rate of the sensor and its vehicle can be sensed by detecting changes in the resonating pattern owing to the Coriolis force acting on the rotating frame. “This technology also gives our DMU30 and DMU11 systems significant immunity to shock and vibration, whereas asymmetric constructions can suffer considerably from real-world impacts and vibrations,” Hughes added. Water Linked demonstrated its short baseline acoustic positioning system, which uses four receivers to track a UUV-integrated locator module. “You don’t have to be within the grid created by the four receivers; they are typically deployed together from a boat or dock about a few metres apart from one another, and they give 100 m coverage in any direction,” explained Torstein Skogseth. “Most other underwater positioning systems cannot work in a highly reflective environment such as a tank, but our proprietary software algorithms filter and calculate to correct the interference for such environments.” The system is aimed at divers and smaller UUVs. “We have found that the advances brought about by modern comms technology have not yet really been applied to underwater acoustic systems. Using such technology is what really enabled us to go smaller with our modules,” Skogseth added. Copenhagen Subsea showcased its range of rim-driven thrusters for underwater vehicle propulsion, including its newest and largest thruster, the VXL. This has seven blades of 236 mm in diameter, weighs 12 kg in the water, and is rated to a depth of 3000 m. “In the VXL and our other thrusters, the stator is placed in the outside rim of the thruster’s duct,” Christian Martinez Tyroll explained. “That provides the stator with a huge cooling surface, so that when operating in water the thruster is able to provide a lot of thrust without overheating.” Besides the VXL, Copenhagen Subsea also manufactures the 83 mm VS, the 131 mm VM and the 168 mm VL for subsea vehicles, each of which comes with a customised motor controller configured according to their anticipated applications and environments. “We also use surrounding seawater to lubricate the bearings, so we have no oil inside, so no risk of spillage,” Tyroll said. “Furthermore, the water that runs between the rotor and the stator creates a thin water film that suspends, and keeps in place, the rotor inside the thruster. “The result is that no two mechanical parts are touching each other during operation. There is no risk of entanglement, and that reduces costly downtime dramatically. The rotor is in fact the only moving part in the thruster.” Oceanology International 2018 | Show report Unmanned Systems Technology | April/May 2018 Silicon Sensing’s DMU30 IMU has ring gyros optimised for navigation Part of the Water Linked short baseline acoustic positioning system Copenhagen Subsea rim-driven thrusters have a huge cooling surface